In earlier experiments, the present inventor studied vegetative propagation on a field scale in several southern warm season turfgrasses, particularly the bermudagrasses. Many warm season grasses are sterile hybrids and do not set seed, or set enough seed, to be propagated economically by seed. Hence, many of these grasses are reproduced vegetatively by “sprigging.” Sprigs are a material harvested from verticutting mature fields of sod, or obtained from shredding bulk sod of the grass as, e.g., in Lastinger et al U.S. Pat. No. 6,223,662. Alternatively, these warm season grasses may be reproduced vegetatively by “plugging”, i.e., planting what are typically three-inch square pieces of grass sod into soil.
Another method of propagating grasses other than by “sprigging”, “plugging” or seeding was disclosed in the present inventor's earlier issued patents U.S. Pat. Nos. 5,899,020, 5,806,445, and 6,286,253. In the system described in those patents, whole pieces of sod of the cultivar to be propagated are separated into pieces of vegetative planting material (or VPM). Sod used for VPM production is typically grown over plastic sheeting or any root-impervious surface, making it possible to reduce soil contamination from nematodes, deleterious insects, and pathogenic micro-organisms, and also to maintain the integrity of the primary rooting system. VPM is produced over plastic sheeting from “whole sods” which are comprised of complete root systems, stems, stolons, rhizomes, ramets, crowns, culms, leaves, and all. Sods grown over plastic sheeting can also be harvested much earlier than sods grown directly on soil as indicated in my earlier patents. Being able to harvest sods for VPM production much quicker is a very distinct advantage in the production of this new type of vegetative propagating material.
In the methods of the earlier patents mentioned above, sods were separated into vegetative pieces by shredding or milling whole pieces of mature harvested sod. I discovered that this method of separation destroyed too much meristematic tissue, diminishing the quantity and vigor of viable vegetative planting material. Accordingly, in an effort to improve upon this earlier method of separation, I discovered a much less damaging method of producing vegetative planting material which, consequently, improved significantly the yield or quantity of viable vegetative planting material obtained. Concomitantly, I discovered: (a) an entirely new form of vegetative propagating material which I have named Grass Plantlets; (b) a method for producing them; and (c) a new methodology for the rapid replication of newly planted cultivars. These and other aspects of the invention are described in more detail below.